elements and compounds lessons 1-3

Atoms of different elements join to make a molecule.. Details tell more about the main idea.. The main idea is that all matter is made from elements.. The Periodic Table Elements are the

Elements and

Compounds

Lessons 1–3

Copyright © by Harcourt, Inc.

All rights reserved No part of this publication may be reproduced or transmitted in

any form or by any means, electronic or mechanical, including photocopy, recording,

or any information storage and retrieval system, without permission in writing from the

publisher

Requests for permission to make copies of any part of the work should be addressed to

School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando,

Florida 32887-6777 Fax: 407-345-2418.

HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the

United States of America and/or other jurisdictions.

Printed in the United States of America

ISBN-13: 978-0-15-349188-7

ISBN-10: 0-15-349188-4

1 2 3 4 5 6 7 8 9 10 179 15 14 13 12 11 10 09 08 07 06

If you have received these materials as examination copies free of charge, Harcourt

School Publishers retains title to the materials and they may not be resold Resale of

examination copies is strictly prohibited and is illegal.

Possession of this publication in print format does not entitle users to convert this

publication, or any portion of it, into electronic format.

Visit The Learning Site!

These gold bars have only

one kind of element in them.

What Are

What Are Atoms and

Atoms and Elements?

2

An atom is a very small unit

of matter

Scientists use the periodic

table It tells them a lot about

the elements

Atoms of different elements

join to make a molecule.

These compounds are made

from different elements

3

This salad is made from a

mixture of different fruits.

The shape of this lizard is a

physical property

READING FOCUS SKILL

MAIN IDEA AND DETAILS

The main idea is what the text is mostly about

Details tell more about the main idea.

The main idea is that all matter is made from elements Look for details about how elements are combined into mixtures and compounds

Atoms and Elements

An atom is the smallest unit of an element It is the smallest

part that has that element’s properties An element is the

simplest form of matter It has only one kind of atom Oxygen

is an element Oxygen is made only of oxygen atoms

Atoms can be broken down into smaller parts Atoms are made of protons, neutrons, and electrons All protons are

alike All neutrons are alike All electrons are alike They do not

have properties of any element

This oxygen atom has 8 protons and

8 neutrons.

The lead of a pencil is made of

graphite This is a soft form of carbon C

The ways protons, neutrons, and electrons combine

form an element’s properties They combine in different

amounts in each element Each element has a different

number of protons The number of protons tells scientists

which element it is

Atoms have the properties of the element they are part of

Carbon atoms have the properties of carbon

There are about 100 elements But only a few are found in

their pure states Scientists give each element a short name

They use one to three letters to name each element Carbon

is C Sodium is Na.

What makes an element different from other elements?

D A diamond is made of

almost pure carbon

All living things have carbon in them C

The Periodic Table

Elements are the building blocks of matter From only about

100 elements, millions of things are made Everything on Earth

is made from different groups of elements

Atoms of each element have a certain number of protons

Each atom of hydrogen has just one proton Each atom of iron

has 26 protons The number of protons in an atom is called its

atomic number.

Scientists use a chart called the periodic table In this chart,

the atomic numbers of all elements are shown Each element

has its own box in the table In that box is the atomic number

of the element Also in the box are the element’s name and

symbol

How many elements are in the periodic table?

The Periodic Table

Water is made of 2 hydrogen atoms and

1 oxygen atom.

Molecules and Compounds

Most elements are seen as parts of compounds A

compound is a substance made of two or more elements The

elements have been joined chemically A formula tells what is

in a compound It shows how many atoms of each element

are in the compound

of hydrogen and oxygen atoms Both of these are elements

The smallest piece of the compound water is a water

molecule A molecule is the smallest unit of a compound

What elements make up a water molecule?

Physical Properties

Physical properties describe a substance They tell what

a substance is like by itself Water is wet Wood is hard These

are physical properties

Some physical properites cannot be seen directly

Temperature is a physical property But you cannot see it Mass

is a physical property But you cannot see it Both mass and

temperature have to be measured

8

The element sodium (Na) is a metal The element chlorine (Cl) is a gas They com- bine chemically to make NaCl, or salt.

A mixture is a combination of two or more substances In a

mixture, the substances themselves are not changed Each part

of the mix could be separated out again

Most materials found in nature are mixtures Sand and air

are both mixtures

In what form are most materials found in nature?

9

Complete this main idea statement.

1 are the building blocks of matter.

Complete these detail statements.

2 Scientists use the to learn about

Nitrogen boils at very low temperatures That

is a physical property.

Metal is used to build things

that need to last a long time

This lump of coal is made of

carbon, a nonmetal.

What Are

What Are Metals?

10

2

This statue is made of bronze

Bronze is a metal alloy.

The aluminum in this can is

very malleable.

11

Computer chips are made from

silicon, a metalloid.

READING FOCUS SKILL

MAIN IDEA AND DETAILS

The main idea is what the text is mostly about

Details tell more about the main idea

The main idea is that metals and nonmetals have different properties Look for more details about the properties of metals and nonmetals

Metals and Nonmetals

A metal is a substance that easily conducts heat and

electricity This means that metals heat up quickly Electricity

passes through them easily

About 75% of all elements are metals

Copper is used for wires.

This is because it is a good conductor of electricity B

Copper is a metal.

Metals are malleable They can be hammered or rolled into

thin sheets They can be made into different shapes

Carbon is a nonmetal Nonmetals do not have the

properties of metals Nonmetals do not conduct electricity

well They do not conduct heat well

How are metals different than nonmetals?

Mercury is a metal It remains

a liquid at room temperature.

What are two physical properties of metals?

Iron is a good conductor of heat It is often used to make cooking pans

Seeing Metal Atoms

Atoms are very small! Scientists must magnify atoms in order

to see them They use special microscopes

Most microscopes magnify things about 1,000 times An

electron microscope can magnify more than 50,000 times

Scientists can see very tiny objects, like cells Another powerful

microscope is called a scanning tunneling microscope, or STM

This microscope lets scientists look at atoms a different way It

makes images based on how electrons move The atoms in a

solids are arranged in set patterns This is called an array

Scientists can now use an STM to move single atoms to the

surface of a metal They hope someday to make new materials

this way

How does seeing atoms help scientists?

D This scientist is using

an electron scope Images are viewed on a screen.

micro-15

A This bell is made of brass It

does not corrode easily.

Alloys and Metalloids

Steel is an alloy An alloy is a solid solution One way

to make an alloy is to combine metals Another way is to

combine a metal and a nonmetal An alloy has properties

different from the materials in it

Iron is the main metal in many steel alloys But iron is not very hard It becomes harder when carbon is added to make

steel

Bronze is an alloy made from mixing copper and tin Bronze

is harder and stronger than copper Many large statues are

made of bronze They can stay outside for a long time and not

corrode, or break down.

16

Metalloids are elements They have some of the properties

of metals They have some of the properties of nonmetals

Silicon is a metalloid

Silicon is less malleable than metal It conducts electricity,

but not as well as copper The flow of electricity can

be controlled in silicon Metalloids like this are called

semiconductors Semiconductors are used in computers and

CD players

What is the main metal in many steel alloys?

17

Complete this main idea statement.

1 is a substance that easily conducts

electricity and heat

Complete these detail statements.

2 Metals are They can be hammered or

rolled into shapes

3 An is made from different metals, or a metal

and a nonmetal

4 A has properties of both metals and

nonmetals

Review Review

The elements used in making steel alloys differ

They are changed to make

an alloy better for the use

it will have.

What Are the

What Are the Properties

of Some

of Some Common Substances?

18

3

The sand in this sand castle is a

solid

19

READING FOCUS SKILL

MAIN IDEA AND DETAILS

The main idea is what the text is mostly about

Details tell more about the main idea.

The main idea is that many substances have similar properites Look for more details about the properties of common substances

Common Gases

Air is invisible Air is not an element or a compound Air has

no chemical formula It is a mixture of gases

A gas is a state of matter In a gas, matter has no definite

shape It has no definite volume, or amount either

substances to burn They burn when they mix with oxygen

Oxygen 21%

Nitrogen 78%

Argon 0.93%

Carbon dioxide about 0.035% Other gases

about 0.035%

Gases in the Atmosphere

Oxygen 21%

Argon 0.93%

Carbon dioxide about 0.035% Other gases

about 0.035%

Nitrogen 78%

Another form of oxygen is ozone (O3) There is ozone

in Earth’s upper atmosphere Ozone helps keep Earth at a

constant temperature

Hydrogen is another gas It is the most common element in

the universe

Helium is a gas that is lighter than air It is used in weather

balloons and blimps

breathe out, you exhale mostly carbon dioxide.

Why doesn’t air have a chemical formula?

21

This balloon is filled with helium

Helium weighs less than air, so

the balloon floats B

Common Liquids

A liquid is a state of matter In this state, matter has a

definite volume But it has no definite shape

Water is the most common liquid on earth The oceans cover more than 70% of the earth Ocean water is salt water

Water is the only compound on Earth that can be found in all three states Water can be a liquid It can be a gas (water

vapor) Or it can be a solid (ice)

These monkeys in a hot spring have ice on their heads

Water is seen in all three states here. B

Mercury was used

in thermometers for many years.

When most liquids are cooled, their particles get closer

together They contract, or take up less space Water contracts

until it reaches about 4 degrees centigrade (39° F) As it cools

further, it expands, or takes up more space

As water molecules change into ice, they form rings The

rings take up more space That is why ice takes up more space

than water

Mercury is the only metallic element that is

liquid at normal temperatures It was used in

thermometers But mercury is poisonous, so

it is not used any more Alcohol is used now

What are some unusual properties

of water?

Common Solids

The element carbon is a solid A solid is a state of matter It

has a definite shape and a definite volume

Carbon is the sixth most common element in the universe

There are millions of compounds that have carbon in them

Charcoal, the “lead” in a pencil, and diamonds are all carbon

Coal, petroleum, and natural gas are compounds They are made of carbon and hydrogen When oxygen is added to

carbon and hydrogen, sugars are made Corn syrup and table

sugar are two of these sugars

The “lead” in a pencil is called graphite In graph- ite, the carbon atoms are joined in flat layers.

The most common solid on Earth is Earth itself

Copper and nickel come from Earth They are used in

making coins Stones for fireplaces also come from Earth

Aluminum for cans and silicon for glasses come from Earth’s

crust

Gemstones, like rubies and diamonds, are mined from under

the ground Metals for cars and ovens come from materials

found in Earth’s crust

Where do most of the objects you use originally come from?

The atoms in a mond are arranged in

dia-a wdia-ay thdia-at mdia-akes it very hard.

Molecules of Life

Without carbon, Earth would be lifeless Even tiny bacteria are 50% carbon Carbon is the basic building block of life

About 98.8% of the human body is made from 6 elements

Oxygen, at 65%, makes up the largest amount Carbon

is second, at 18.5% Hydrogen, nitrogen, calcium, and

phosphorous are the other four

Each element is needed for good health

26

Red blood cells get their color from a molecule called hemo- globin Each molecule has four atoms of iron B

DNA is in every cell of the body It makes sure that when

new cells are made, they are exactly like the old ones But it

is made from just a few elements

The DNA molecule looks like a twisted ladder Each

colored ball in this picture of DNA shows a different

element

What element is the basic building block of the molecules of life?

27

Complete this main idea statement.

1 All comes in three states: solid, liquid, or gas.

Complete these detail statements.

2 A has no definite shape and no definite

DNA is found in the nucleus of every cell

in the body.

GLOSSARY

alloy (AL•oy) A solid solution in which a metal or a nonmetal

dissolves in a metal

atom (AT•um) The smallest unit of an element that has the

properties of that element

compound (KAHM•pownd) A substance made of two or more

liquid (LIH•kwid) The state of matter that has a definite

volume but no definite shape

malleable (MAL•ee•uh•buhl) Easy to shape or to form

metal (MET•uhl) A substance that transfers heat and electricity

well and is malleable

metalloid (MET•uh•loyd) A substance that has some of

the properties of a metal and some of the properties of a nonmetal

mixture (MIKS•CHER) A combination of two or more different

substances

molecule (MAHL•uh•kyool) A group of two or more atoms

that are joined

nonmetal (nahn• MET•uhl) A substance that does not transfer

heat and electricity well and is not malleable

periodic table (pir•ee•AHD•ik TAY•buhl) A table that shows

the elements arranged by their atomic numbers

physical property (FIZ•ih•kuhl PRAHP•er•tee) A trait—such as

color, shape or hardness—that describes a substance by itself

solid (SAHL•id) The state of matter that has a definite shape

and a definite volume